Evacuation process.



H. C. SNOOK.

EVACUATION PROCESS.

APPLICATION FILED 06118. 1912.

1,166,792. Patented Jan.4, 1916.

2 SHEETS-SHEET l.

WlfivEssEs A $44 %INVE?IT %?M c,6 i 7 BY H. c. suoox. EVACUATION PROCESS.

APPLICATION FILED OCT-8| I912.

Patented Jan. 4 1916.

2 SHEETS-SHEET 2.

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J V gw-llTNssEsee/ Z To all whom it may concern HOMERCLYDE snoox, or CYNWYD, PENNSYLVANIA.

EVACUATION Pnocnss Be it'known that I, HOMER CLYDE SnooK, 1 a citizengoftlie United States, residing at Cynwyd, State of--Pennsylvania,-haveinvented certain new and. useful Improvements in Evacuation Processes, of which the a following ,is a specification.

My invention relates to a processof ex hausting or evacuating X-ray tubes, Crookes,

through filaments-or conductors such as, for? example, in incandescent electric-lamps.

his the obj ect of my invention to provide a process for evacuating tubes, bulbs, etc., of

bulbs or lamps.

the character referred to, which will materially shorten the time consumed in evacuation, cheapen the process of evacuation, and produce a final vacuum which will improve the operating characteristics of; the tubes,

To these ends my invention resides invthe process and apparatus hereinafter described and claimed.

For an illustration of some of the forms? my apparatus may take'for carrying out my' process reference is to. be had to the accom I panying drawings'in which: Q

. Figure l'isa diagrammatic View of :appa

ratus for carrying out my process for evacuating, an X-ray tube orthe like. Fig. 2 is a diagrammatic view of apparatus illustrating my process of evacuating incandescent lamp vacuum tube.

bulbs. FigI B is a graphic representation of potential gradient between electrodes of a" Y 1 I l Referring to Flg. 1, X represents the bulb of an X ray tube whoseinterior is incommunicationwith a vacuum pump, not-shown,..

comm

through the connection 1' during the process j of evacuation. The cathode is is in electrical icati-on with the-exterior through {terminal 2 sealed into-the glass of the tube stem 3; and the anode a is shown, by way of example, as supported uponrthe conducting tube 4 in the glass tube stemo and communi .cating with the eiiterior'through the con- I ductor .6 seale'din the .glass-of the stem 5,

The terminal 2 is in electricalcommunication through conductor 7 with 'the terminal 8.ofthe-electricyswitch 9,.and the terminal 6 Specificatien of Letters Patent. v

Amlication filed October 8,

ratemeaa ma;1916.; 1912. sem1no.724,557.

is in communication through conduct0r10-- with the terminal 11 of the'switch' 9.; The= switch 9 may be; thrown to either .off two positions; in theposition shown the switch brings terminals j '8 "and 1.11 into electrical communication with-the terminals 12 and 13,

respectively, and its other position brings its terminals 8 and-1 1 into -.electr ical com; munication withthe terminals-'14 and 15, respectively.- The terminal 12 connects through conductor 16 with thelnid-pointof the s'econdary s of'transformer't. One terminal of the secondary 's. connects by conductor 17 with an electrode 18 of a mercury vapor rectifier 19, another of whose electrodes 20 connects through conductor 21 with the other terminal of the secondary s.

The main mercury puddle 22 of the rectifier Q connects through conductor 23 and ammeter 24 with switch. terminal :13 and connects also w-ithterminal 25 of electric switch 26 which' I is adapted to bring terminal 25 into communication with terminal 27 and toflbring terminals 28 and 29 intocommunication with each other. The ,terminal. 28 connects through ammeter -30 and. adjustable resistmice 31 with one terminal'of the generator.

or source of direct current 32 whosejother andto earth E, The source '32 delivers low through conductor 34 with switch terminal 29, being understood that the arc is started terminal is connected to switch terminal 27;

:85. voltage direct-current to'maintain the ionize 1 --ing; arcbetween themercury puddle 22 and 1 Y the mercury puddle 33 ,"the latter connected by'cau'sin'g the mercury puddles 22 and 33 to come" momentarily into contact with each other, as bytilting the rectifier. 19;

- The atrans'fornaer t is a step-up transformer, each half of the secondary s deliver-.

an alternating currentof 1500 volts, for

example, the difference of potential between the electrodes 18 and 20 being'-therefore'3,000 volts. The primary ';0 of the, transformer-t.

is shown in circuit; through the switch 35' and adjustable resistance 36'yand reversing switch 37 with the generator or source 38. of

alternating current. The reversing. switch 37 simplyservestochange the direction of current-through thep'rimary'p if for any reason any-of the connections in the secondary circuitare..reversed -or wrong. The alternating current delivered by the secondary:.s to the rectifier 19 is'r'ectified into unidirecti-onalcurrent which is then passed 1 through the X-ray tube X as andcfor the purposes hereinafter described.

By throwing the switch 9 down into com munication with'contacts 14 and and-by throwing" the switch over to the left into communicationwith contacts 39 and 40, a source of Very high tension unidirectional current is brought into communication with X-ray tube X through the switch 9 By throwing the switch 35 to the left, as stated,

the transformer t-is cutout of operation and of course thereforeithe rectifier 19. A current from the generator 38 will pass through the primary P of the transformer T Whose high potential secondary S communicates with the rectifying switchR, the latter delivering unidirectional hightension cur-- rent by conductors '41 and 42 through the switch 9to the X-ray tube X. Anysuitable means for supplying high tension unidirectional current maybeprovided, but the transformer T, rectifyingswitch R and generator 38, may be of'the character and 00- operating'as described in my prior Patent No. 954,056. Tn thiscasetheswitch'52 serves to; cut in more or less of 'the' turns of .gthet primary P for securing-difi'erentpotentials" at the terminals of the X-raytube X, and

the adjustable re'sistanc'e 36 may also be em--" plo'yed for current control, purposes. It is! to be understood alsoxthat my" invention. is} not limitedto the employment of a mercury. 1 vapor rectifier such as 19, butthata'riy other suitable means for" delivering moderately high potential unidirectional current to X-ray tube may be employedzi The bulb X of the X-ray tube having been put into communication throughconnecti'on 1 with the 'vacuum-pump, not shown, the; pump is started and'the' air. exhausted: from m the bulb Xfuntil a vacuum of, aboutl milli- -meter of mercury, absolute pressure, is attained. This degree of vacuum is reached after in a relatively short period of T'pumping and to determine when." this degree of vacuum has been reached, thefswitch 9 may ,be thrown down into communication with terminals 14 and -15 and the switch 35 thrown into 'communicationfwith terminals 39 and 40, the switch-.52 beingladjusted to such contact as to cause. delivery from the secondary S a current of a tension of approximately 5,000 volts, or even less. And the switch 37 is thrown into'such position as will make the" anode a of the tube vX the temporary cathode or' negative terminal.

-There will occur around this temporary.

cathode a a cathode or negative glow of about inch thickness, if the vacuum is substantially 1 mlllimeter of mercury. If this glow isthicker an a of an inch, it indicates that the vacuum is too high, and a slight amount of. air may be readmittedcto the tube X until the glow is'substantially of an inch in thickness. of an inch thick- 'bulb or stem 5.

actually 'lnechanicallyremoving the mass of this glow is about the minimum thickness the negative glgw attains, under these conditions. I

v The vacuum having been determined to be' substantially 1 millimeter of mercury, the switch 9 is thrown up into communication with terminals 12 and 13 and the switch 35 removed from terminals 39 and 40 and thrown into the position illustrated in Fig. 1

thereby causing the rectifier 19 to come into 75.1 m

o eration and to deliver current through the ray tube, the target or anode a being again the .negative terminal or temporary cathode. At this time the communication between the tube X' and; the pump is cut off. so

'The application of about 1500 volts to. the

terminals ofthe X tube by means of the rectifier 19 will cause "a negative glow to appear at the temporary cathode (1. And by adjusting the resistance 36, or the ratio of transformation oftransformer t if desired, or both, the girrent through the tube may be increased until the cathode glow spreads i and extends over the entire temporary cathode a and along the stem or tube 4 near to '90 butnot completely reaching the glass of the Foran X-ray tube of, ordinary "size a current of from 1' to 2- .amperes, as determined by ammeter 24, will generally sufiice' for this purpose. This excitation is continued for approximately 3 or 4 minutes, more or less, and the glow extending over the temporary cathode a andtube 4, J as described, heats the same until they attain a red heat, causing occluded gases to be driven off. After maintaining this condition for the 3 or 4 minutes, as stated the connection between the tube X and the pump is again opened, the pumpicontinuing to exhaust gas from the tube Xwhile the current continues to passthrough the tube X. As the vacuum becomes higher. and higher,

due to the continued pumping, the cathode glow extends farther and farther from the temporary cathodea and tube 4'and will finally fill'the entire bulb X, resistance 36 or primary p, or both, havimg been adjusted as the glow extends, until a pressure of from- 3,000 to 5,000 volts is applied to thetube X.

When this state is reached, connection between the bulbX and the pump is again shut off. llhe cathode glow filling the tube to the walls is continued by the continued passage :of current from the rectifier 19. This tube filllng glow is continued for a relatively glow the glass may soften and the tube may collapse, or the local heating of the walls may be so intense as to devitrify the glass. After this whitish glow appears the strength of the current through the tube supplied by rectifier 19.is reduced, as by adjusting resistance 86, sufiiciently to cause the disappearpresent in thebulb. As the vacuum rises,

the current through the X-raytube falls rapidly as will be indicated by the ammeter 24; and the evacuation is carried to a point at which the discharge ceases entirely. At this stage the temporary cathode and supports are still at red heat and the glass walls are hot. The tube X is now exteriorly heated, as in an oven, in'which it may have been placed at the beginning of the process to a temperature of approximately 300 centigrade, the connection with the pump remaining open so that evacuation continues.

Ordinarily the oven reaches the aforementioned' temperature in approximately 20.

minutes, the pumping continuing during this period and for a further period of approximately 5 minutes during which the tube, is maintained at the aforementioned tempera- ,ture.

lVhile continuing the pumping operation,

the temperature of the oven is' gradually lowered from 60 to 80 centigradeduring a minal. These discharges serve as'a test for the degree of vacuum as determined by the appearance of the fluorescence of the glass and by the color and shape of the discharge in the gas. Pumping is continued until the resistance of the tubeas indicated by'the spark gap 57 connected in parallel-with the X-ray tube shows that the proper degree of vacuum has been reached,'the vacuum at this time, because the tube is still hot or. warm, is

lower than the vacuum when the tube is cool. For example, when theresistance of the tube is indicated to be that of a parallel spark gap in the air of a length of from 3 to 4 inches.

with the tube at a temperature of from 60 to- 80 centigrade, the vacuum in the X-ray tube I has attained the proper degree, and nowthe connection 1.to the vacuum pump is sealed off, the tubebeing now permanently disconnected from the pump by the sealing shut of the glass connection 1. The tube is now allowed to cool to the temperature of the room and it will be found that its resistance at room temperature is indicated by a parallel spark gap resistance of 6 or 7 inches'in I length, this resistance of the tube being satisfactory for the production of X-rays. By the process above described the evacuation of the tube may be accomplished in about three quarters of an hour as compared with a period of from 2 to 4 hours by prior methods.

Where an induction coil employing direct current with an interrupter in its primary circuit or other imperfect rectifier is used for supplying the current to the tube in place ofthe rectifier 19, the bad efiects of the imperfect rectification may be more or less overcome by introducing into the X-ray tube, after initial pumping to a pressure of 1 millimeter of mercury or less, hydrogen or other gas chemically neutral with respect to the materials of the anode and cathode within the tube. After allowing the process to rest a few minutes after introduction of the hydrogen or other gas to allow thehy drogen-or other gas to diffuse thoroughly through the tube, connection with the pump is again established and the vacuum again raised to a pressure approximately 1 milli-, meter of mercury. Then the process as hereinbefore outlined is. continued. And even in cases-where rectification is perfect, there is a glow at or surrounding the temporary lanode 7c and if the rate of; liberation of en ergy within the tube be sufiiciently great and if the gas content of the tube is chemically active with the temporary anode mate rial, excessive local heating at one or more rot points on the temporary anode occurs, and 7 this heating may be so intense as t0 raise the neighboring glass to such a temperature as' to cause softenlng or even rupturing ofthe glass; or, in other words, if the rate of liberation of energy in the tube be high enough to produce a certain temperature by anode glow at an eXcrescence-on the tempo rary anode and if the gas content of the tube will at that temperature chemically attack the temporary anode, the locaLheating ocours as stated. To overcome this efiect, hydrogen or other gas chemically neutralwith respect to the temporary anode material may be introduced after the initial. pump ing to a vacuumbf approximatelyl milli- 3 meter of mercury. Then after allowlng the hydrogen or neutral gas to'dltfuse, the

process is continued as hereinbefore first described.

- In Fig; 2 I have shown one form on air paratus-for carrying out my process of" evacuating incandescent lamp bulbs, or the 'vacuo. Here the plurality oflanip bulbs 13' bulbs of any device in which an'electric conductor is traversed by current while in may be simultaneously in communication through the tubes 43 with the tube 44 adapted to be putv into communication with. "a

vacuum pump. "The lamp filaments f are sealed through the bulbs B in'the usual manner and one terminal of each filament is connected to the conductor 45 while the other terminal is connected to the conductor 46 through an adjustable resistance 47. The

conductors 45 and 46 are adapted to be thrown into electricalcommunication with the terminals of the source of current 47' by switch 48. Communicating with the interior of the tube 44, and therefore with the interiors of the bulbs B, is the electrode 49 to which is connected the conductor 50 sealed throughthe glass of thehollow projection .51 sealed to the tube 44 at any suitable point. The conductors 45 and 50 are adapted tobe put into electrical communication with a source of more or less high potential unidirectional current, approximately 1500 volts pressure, such as maybe delivered by a rectifier 19 or equivalent ap'-.

paratus. Here the conductor is shown connected to earth E, though conductor 46 may beso connected instead.

The vacuum pump having been started, the tube 44 is put into communication with it, and the air quickly exhausted from the bulbs 13 until a vacuum of about 1 millimeter of mercury or less is attained then hydrogen or other gas may be admitted to I the bulbs B through tube 44 until the pressure in the bulbs B rises, for example to one half atmosphere pressure. Then pu'mping is resumed and continued until thevacuum again attalns a pressure approxl- "mately 1 millimeter of mercury or less.

Then the conductors 45 and '50 are thrown into communication with the source of unidirectional current of 1500 volts pressure more or less, causing a negative glowaround thefilaments fiwhich are made the negative electrodes 01 cathodes during the process; and the pumping is continued untll suchnegative glow fills the bulbs B. And as in the case hereinbefore described with respect to X-ray. tubes such negative g1ow"filling the bulbs acts both by this heating efiect and mechanical elfect to remove the gases'from the inner walls of the bulbs,.such gases be-' 7 ing removed by the continued I pumping.

The heating oven may now be started: Gonnection from tube 44 to the pump is shut. 0 a and the negative glow'filling thelbulb s is continued until the whitish glow appears.

Then pumping is resumed until the negative,

glow discharge entirely or substantially en.- tirely. disappears. During this time the bulbs have'been rising temperature due igieegea j tothe-rise in temperatureof the"oven," and the heating by the oven is continued as is also the pumping and a currentmay: now be passed through the filamentsff'by closing the switch 48, the current through the filam'ents'being"' continue for some time, The consequent heating of {the} filamentsadrives the tube 44. The result is a final vacuum which is important in improving the operating and life characteristics of incandescent lamps and the 1ike,particular1y 1n the case of incandescent lamps having tungsten or other metallic filaments In Fig. 3 there is a graphic representatlon of the potential gradient, curve 55 representing the potential drop at diflerent points in the gaspath between'negative and positive terminals or electrodes when the gas, such as air, is at a pressure in the neighborhood of.1 millimeter of mercury. This figure is not limitive of myinvention but illustrative only and serves to show that the greatest potential drop is at 56 near the negative electrode whose face is represented M53, 54 representing the face of theposi-' tive electrode, the space between indlcating the distance in gas between the two elec' trodes. Ordinates' of the" curve represent potentials in the gas between. the electrodes.

Inasmuch 'as the potential drop for a given current is far greaterat or near the negative electrode it follows that the greatest part of the energy is there dissipated and for that reason the negative glow is best utilizable for the purposes herein'described.

WhatTclaim is: i i -l. As an improvement in'the art of enhausting bulbs, the .method, whichconsists in partiallyexhausting a bulb, passing energy through the 'remanent atmosphere between an anode and cathode, heating- .said cathode by said energy, and further exhausting said bulb during passage of energy until the cathode glow fills said bulb and acts upon the inner walls thereof;

2. As an improvement in the art of exhausting bulbs, the method which consists inpartiallyfexhausting a bulb, passing energy'through the remanent atmosphere be- :-tween a'nj ano de and cathode, heating said [cathode by sald energy, further exhausting fsaid' bulb during passage of energy until exhaustion for a period-during which said the cathode glow fills said bulb and acts upon" the inner walls thereof, interrupting.

said bulb during passage of energy until the cathode glow fills said bulb and acts upon the inner walls thereof, interrupting exhaustion for a period during which said bulb filling glow continues, and thereafter resuming exhaustion until said glow disappears. v

In-AS an improvement in the art of exhausting bulbs, the method which consists in partially exhausting a bulb, passing energy through the remanent atmosphere ,be-,

tween anv anode and cathode,-heating said cathode by said energy, further exhausting said bulb during passage-of energy'until the cathode glow fills said bulb and acts upon the inner walls thereof, interrupting exhaustion for a period during which said bulb filling glow continues, thereafter resuming exhaustion until said glow is re' duced, and exteriorly heating the bulb.

5. As an improvement in the art of'exhausting bulbs, the method which consists in impressing electrical potential of three hundred volts or more upon electrodes sepa rated in the atmosphere of a'bulb, and reducing the pressure within said bulb to the order of one millimeter of mercury until "saidpotential produces at the cathode a glow substantially one-sixteenth of an inch ing the pressure.

' glow in thiclmess for heating said cathode, and thereafter further exhausting said bulb.

'- 6. As animprovement in the 'art of exhausting bulbs, the method which consists in impressing electrical potential of three hundred volts or more upon electrodes separated in the atmosphere of sand bulb, reducorder of one millimeter of mercury-until said potential produces at the cathode a substantially one-sixteenth of an inch in thickness for heating said cathode, main: tainin said glow for a period of time, and

,therea ter further reducing the pressure within said bulb;

7. As an improvement'm the art of exhausting bulbs, the method which consists ergy in partially exhausting a bulb, passing enof a unidirectional current through said bulb, adjusting the amountof sald-energy to cause a glow spreading over an electrode within said bulb to heat said electrode and resuming exhaustion of said bulb while [continuing passage of ."said bulb Jwherebyfsaid glowextends and finally saidqbulb, I

within said bulb to thesai-d-ener throu h gy g atmosphere of said As an improvement in the art of exhaustlng bulbs, the method which consists in partially exhausting a bulb, passing energy of a unidirectional current through said bulb, adjusting the amount of said energy to cause a glow spreading overan electrode Within said bulb to heat said electrode, resuming exhaustion of said bulb while continuing passage of said energy through said bulb whereby said glow extends and finally fills said bulb, and discontinuing exhaustion while maintaining said bulb filling glow for a period sufficient to heat said bulb.

' 9. As an improvement in the art of ex- I hausting bulbs, the method which consists in partially exhausting a bulb, passing en-v ergy of a unidirectional current through said bulb, adjusting the amount of said energy to cause a glow spreading over an electrode within said bulb'to heat said electrode, resuming exhaustion of said bulb while continuing passage of said energy through said bulb whereby said glow extends and finally fills said bulb, discontinuing exhaustion and maintaining said bulb filling glow fob a suitable period, and thereafter resuming exhaustion.

10. As animprovement in the art of exhausting bulbs, themethod which consists in partially exhausting a bulb, passing 'en-.'

ergy of a unidirectional current through said bulb, adjusting the amount of said energy to cause a glow spreading over anelec trode within said bulb to heat said electrode, I

resuming exhaustion of said bulb while eontinuing passage of said energy through said bulb whereby said glow extends and finally able period, and thereafter resuming exhaustion untilsaid glow disappears. I 11. As an improvement in the art of exhausting bulbs, the method which consists in partially exhausting a bulb, passing energy of a unidirectional current through said bulb, adjusting the amount of-said energy to cause a glow spreading over an elec-' trode within said bulb to heat said electrode,

resuming exhaustion of said bulb while con tinuing passage of said energy through said bulb whereby said glow extends and finally fills said bulb, discontinuing exhaustion and maintaining said bulb filling glow for a suitable period, and thereafter resuming exhaustion until said glow disappears, exteriorly heating said bulb during continued exhaus tion, and sealing ofi said bulb. 4

.12. As an \improvement in the a rt of exhausting bulbs, the method which consists in partially exhausting a bulb-to a pressure fills said bulb, discontinuing exhaustion and -maintaining said bulb filling glow for a suit impressingupon electrodes separated inthe f I bulb an electric potential I "of three hundred volts or more for producof the order of one millimeter of mercury, 1

, ingl a glow at the'cathode to heatthe same,

it and thereafter continuing exhaustion and 1 increasing said potential until said glow fills said bulb.

13; .As an improvement in the-art of exhausting bulbs, the method which consists inpartially exhausting a bulb to a' pressure v of the order of one millimeter of mercury,

impressing upon electrodes separated in the atmosphere of said bulb an electric potential of three hundred volts or more for produc-' ing a glow at the cathode to heat the same, thereafter continuing exhaustion and, increasing said potential until said glow fills said bulb, and-discontinuing said exhaus tion and continuing said glow.

14k. As an improvement in the artof ;ex-

hausting bulbs, the method which consists in partially exhausting said bulb to a pressure of the order of one millimeter of mer- .cury, impressing upon electrodes separated in the atmosphere of said bulb an electric potential of three hundred or more volts for i producing a glow at the cathode to heat the same, thereafter continuing exhaustion and ;"increasing said potential until said glow fills said bulb, dis continuing said exhaustion and continuing saidglow, and thereafter I resuming exhaustion until said glow disappears. 1 H

' 15. As an improvement in the art of exhausting bulbs, the method which consists in partially exhausting a bulb to a pressure of'the order of one millimeter of mercury,

impressing upon electrodes separated in the atmosphere of said bulb an electric potential of three hundred volts or more for producing a glow at the cathodeTto heat the same,

thereafter continuingfexhaustion and in creasing. said potential until said glow fills said bulb, dis-continuing said exhaustion and continuing said glow, thereafter resumingexhaustion until said-glow disappears,

and exteriorly heatingsaid bulb during said continued exhaustio 16. As an improvement in the art of ex hausting bulbs, the method which consists in partiallyexhausting a bulb to a pressure of the order of onmillimeter of mercury,

impressing. upon electrodes separated in the atmosphere. of said bulb an. electric potential I ofthree hundred volts or more for producifng a glow-at the cathode to heat the same,

thereafterf'continuing. exhaustion and in-i creasing. saidp'otential until said glow fills saidbulb, dis-continuing said exhaustion andecontinuing said glow,-thereafter resuming exhaustion until said glow disappears,

: exteriorly heating -said bulb, allowing said bulb to cool,'and while: cooling continuing said exhaustion.

17; As en improvement in the artof exhausting bulbs," the method which consists in partially exhausting abu-lb, impress-- amaze r potential-o gmore than three hundred-voltsupon electrodes separated in the atmosphere, of said bulb, whereby the oathode is heated while the pressure in said bulb is substantially one millimeter of mercury,

" and thereafter further exhausting said bulb.

18-. As-an improvement in theart of evacuating bulbs, themethod which consists in partially exhausting a bulb, impressing an electric potential upon electrodes separated in the atmosphere of said bulb to heat the cathode, continuing exhaustion and inbulb, and adjusting said potential until a change of color of said glow to a whitish "color is. impending.

20. As an improvement in the art of evacuating bulbs, the method which consists in partially exhausting a bulb, impressing upon said bulb electrical potential whereby a. cathode glow of bluish color fills said bulb, adjusting said potential until a change of color of said glow to a whitish color is impending continuing said glow for a period of time, and thereafter resuming ex- 'haustion until said glow disappears.

21. The method of exhausting an X-ray tube, which consists in partially exhausting the tube, impressing an electric potential upon electrodes within said tube, the anticathode serving as cathode to heat the same to redness with a glow confined thereto, thereafter further exhausting the tube until the cathode glow fills the tube to operate upon the inner walls'thereof, discontinuing exhaustion and continuing said last named glow, and thereafter further exhausting said tube. u v. 22. The method of exhausting an X-ray tube, which consists in partially exhausting the tube, impressing, an. electric potential upon electrodes within said tube, the anticathode serving as cathode to heat the same to redness with a glow confined thereto, thereafter' further exhausting the tube until the cathode glow fills the tube to operate up the innner walls thereof, discontinuing exhaustion and contir'ming said last named glow, and thereafter continuing exhaustion of said tube and simultaneously 'exteriorly heating the same. 1

23. The method of exhausting an X-ray tube, which consists in partially exhausting the tube, impressing an electric potential upon electrodes within saidtube, the anticathode serving as cathode'to heat the same i toflredness with a glow confined Ither'eto,

thereafter further exhausting the tube until In testimony whereof I have hereunto the cathode glow fills the tube to operate afiixed my signature in the presence of the 10 upon the inner walls thereof, discontinuing two subscribing witnesses.

exhaustion and continuing said last named HOMFR CLYDE SNOOK glow, thereafter continuing exhaustion and J 3 simultaneously eXteriorly heating the tube, Witnesses:

allowing the tube to cool, and during cool- FLORENCE RUSH,

ing continuing exhaustion. ELEANOR T. MGCALL. 

